11.3.1 The implementation of graph panes

One of the major uses the CAPI itself makes of pinboard-objects is to implement graph panes. The
graph-pane
itself is a
pinboard-layout
and it is built using
pinboard-object
s for the nodes and edges. This is because each node (and sometimes each edge) of the graph needs to react individually to the user. For instance, when an event is received by the
graph-pane
, it is told which pinboard object was under the pointer at the time, and it can then use this information to change the selection.

Create the following
graph-pane
and notice that every node in the graph is made from an
item-pinboard-object
as described in the previous section and that each edge is made from a
line-pinboard-object
.

(defun node-children (node)

(when (< node 16)

(list (* node 2)

(1+ (* node 2)))))

(contain

(make-instance

'graph-pane

:roots '(1)

:children-function 'node-children)

:best-width 300 :best-height 400)

Figure 11.5 A graph pane with pinboard object nodes

As mentioned before,
pinboard-layout
s can just as easily display ordinary panes inside themselves, and so the
graph-pane
provides the ability to specify the class used to represent the nodes. As an example, here is a
graph-pane
with the nodes made from
push-button
s.